The present invention relates to construction engineering and more particularly, to pneumatic percussion tools for driving in rod-shaped elements.
The present invention will be most useful for driving into the ground grounding electrodes, anchor piles, etc. i.e. such rod-shaped elements whose cross section is small in comparison with their length.
Known in the art are several types of mechanisms for driving rod-shaped elements into the ground.
Known in the prior art is a hydraulic mechanism for driving rod-like grounding electrodes into the ground. This mechanism consists of a hydraulic power cylinder with a piston on both sides of which there is a hollow rod receiving the electrode being driven in. Mounted in the upper portion of the cylinder coaxially with the rod is a guide provided with a spiral slot throughout its length, said spiral slot having a steep pitch. On the external surface of the rod there is a fixed pin entering the spiral slot of the guide. Rigidly fixed to the lower free end of the rod is a self-wedging clamp. The shell of the power cylinder is secured by clamps to the mast of an electric transmission line or to the frame of a construction mechanism, e.g. a tractor. The service fluid can be supplied into the upper or the lower space of the hydraulic power cylinder.
At the initial stage of operation the rod is lifted to the upper position and the electrode is interted into it to bear against the ground. Then the fluid is fed into the upper space of the cylinder and the piston goes down together with the rod. Meanwhile, the clamp holds the electrode rigidly so that the latter moves down together with the rod. Going down, the pin slides through the spiral slot of the guide and imparts additional rotary motion to the rod and electrodes. As the piston reaches the lower position, the fluid starts entering the lower space and raises the rod. The clamp releases the electrode and goes up with the rod without the electrode. Upon reaching the uppermost position the rod again starts forcing the electrode down.
A disadvantage of the prior art hydraulic mechanism resides in its large size and in the necessity for fastening it to a solid support or to the frame of a construction mechanism. Besides, driving of rods into a solid or frozen ground by this mechanism is either difficult or altogether impossible due to a static nature of the load applied to the rod being driven in.
Also known in the prior art are rotary mechanisms for screwing rod-shaped elements into the ground, for example a hand-operated mechanism based on an electric drill. This mechanism consists of an electric drill with a reduction unit whose high-speed shaft is connected with the drill shaft. The low-speed shaft of the reduction unit is hollow and carries a self-wedging clamp on its lower end. Fastened in the upper portion of the reduction unit, coaxially with a low-speed shaft is a housing in the form of a tube.
The electrode is inserted into the housing, passed through the hollow low-speed shaft and the clamp. Then the electric drill is switched on. Rotation is transmitted from the electric drill via the reduction unit and the self-wedging clamp to the electrode. The force for driving in the electrode is built up by hand. As soon as the clamp reaches the ground surface the drill is switched off, moved up along the electrode and the screwing motion is resumed.
A disadvantage of this prior art mechanism resides in that the driving-in force is built up by hand which denies the possibility of attaining strong driving-in forces. Besides, this mechanism is not adapted for driving electrodes into solid and frozen soils.
Another prior art pneumatic percussion tool is intended to drive rod-shaped elements into the ground. This mechanism comprises a shell with a clamp rigidly fixed in its front portion. Located inside the shell with a provision for axial reciprocation is a stepped ram. The tail end of the shell is closed by an extension which has air admission and discharge holes. The stepped ram together with the shell forms the front working chamber while together with the extension it forms the rear working chamber. The rear working chamber is in constant communication with compressed air supply whereas the front working chamber is put periodically in communication with the rear working chamber and the atmosphere.
The percussion mechanism is secured by the clamp to the upper end of the rod-shaped element. When the compressed air supply is turned on, the stepped ram starts reciprocating and deals blows to the front portion of the shell. Under the effect of these blows conveyed through the shell and the clamp, the rod-shaped element penetrates into the ground.
A disadvantage of the known pneumatic percussion mechanism resides in that it is adapted for striking only the butt end of the rod-shaped element which denies the possibility of driving in rod-shaped elements whose cross section is infinitely small in comparison with their length because they are distorted in the process of being driven in.
Another prior-art pneumatic percussion mechanism comprises a hollow cylindrical shell with an extension and a front portion accommodating an axially-reciprocating stepped ram.
The small-diameter step of the ram interacts with the extension, the butt end of said ram forming with said extension a rear variable-volume working chamber which is in constant communication with compressed air supply. In the front portion of the shell the stepped ram forms a front variable-volume working chamber which communicates through the axial hole of the stepped ram with the rear working chamber when the ram is in the foremost position and with the atmosphere through the longitudinal channels on the external surface of the large-diameter step of the ram when the latter is in the rearmost position. The stepped ram strikes the shell as it reciprocates in the shell under the force of compressed air fed into the working chambers. The stepped ram moves owing to the difference in its areas at the sides of the front and rear working chambers subjected to the pressure of compressed air.
A disadvantage of the known pneumatic percussion mechanism consists in that the percussion mechanism is secured in the upper portion of the rod-shaped element for driving it into the ground. The rod-shaped element penetrates into the ground under the force of the blows dealt to its butt end. Therefore, the known percussion mechanism is not suitable for driving in rod-shaped elements whose cross section is infinitely small in comparison with their length since said elements are apt to be distorted in the course of the driving-in process.